A number of communication networks are currently utilized in transmitting information including voice and data. Different network channels include CDPD (cellular digital packet data), satellite, SMR (specialized mobile radio), FM-subcarrier, DAB (digital audio broadcast), infrared and two-way messaging. The network channel that is accessed for information transfer depends on its availability in the geographic region of interest.
However, these numerous and quality-diverse communication links available for use in different geographic regions engender a new set of problems that must be faced. Chief among these relates to the reliability of the link or links that might be utilized for a predetermined communications application, particularly where the information transfer involves a mobile unit, whose position changes during the transfer. Unlike communication systems that typify the prior art in which the reliability or stability of a communication link is virtually taken for granted, the present invention involves network channels that, depending on the conditions, can experience inconsistencies or discontinuities during the particular information transfer.
In connection with addressing these reliability issues, the inventors of the present invention have identified additional parameters as being germane to the process for selecting among different network channels for the transfer of information. These parameters include the bandwidth of the available channel and parameters related to the quality and/or quantity of the information or data being transferred, such as packet loss, packet latency and packet jitter. Bandwidth refers to the information transfer capacity of the channel and is definable in terms of a transfer rate, such as bits/second. Packet loss relates to the number of packets that are lost as a function of the number of packets that are received. Packet latency refers to the typical or average one-direction or end-to-end packet transfer time. Packet jitter refers to the variation in inter-packet receive times. Important additional factors or parameters to be taken into account as part of the network channel selection process relate to the cost of transfer including factors such as the network channel cost per packet and any channel setup cost. In view of these many parameters that can be considered when a channel is selected, the selection process for obtaining a desired or optimum network channel can be a complicated task.
The channel selection process is made more complicated and difficult when the transmitter and/or receiver of the transferred information is part of a mobile unit. In such a case, because of the movement of the mobile unit, such as a vehicle, a presently accessed network channel may no longer be available for use because of the new geographic position of the mobile unit. That is, the presently utilized network channel may not be available in the new location of the mobile unit. The network channel selection process is rendered even more complicated when, due to the different geographic position of the mobile unit, a previously unavailable channel is now available to the mobile unit. This previously unavailable channel may be more desirable for the information transfer that is currently under way.